The throughput quantity of transverse systems (shears, stacking devices) and presses (loading systems, feed systems) is a strong function of the transport speed of the corresponding conveyor system. This is particularly true with regards to large transfer presses. The conveyor systems employed must be so constructed that damage to the sheet plates transported, which can be caused by such diverse factors as contact with transport rollers, limit stops or guide rails, is substantially avoided. In addition to the known, purely mechanical conveyor systems of the type having transport carriages, roller tables, belts, and rail-guided carriages, it is also known to construct a conveyor system employing magnetism as a motive force. In such a system, metallic plates consisting of magnetic material (i.e., if not actually magnetic, then at least susceptible to attraction via a magnetic field) are magnetically advanced through the conveyor system. The magnetic field of the stator of a linear motor advances the plates, which form the rotor of the linear motor. In this system, air nozzles are arranged behind and in front of the linear motor along the direction of conveyance.
The air emerging from the air nozzles produces an air cushion between linear motor (stator) and plate (rotor) that prevents the plate from contacting the linear motor. The plate is accordingly moved without contact with the stator part of the linear motor. Such a device is set forth in U.S. Pat. No. 4,077,507, the contents of which are incorporated herein by reference in their entirety. The above-mentioned device can achieve high transport speeds but has the disadvantage that, due to the arrangement of the air nozzles in front of and behind the linear motor, the largest forces are exerted on the plates in the air nozzle region, so that undesired bending occurs approximately in the middle, at the linear motor. The properly positioned guidance is made extremely difficult due to the varying distribution of pressure in the air cushion; the proper coordination and positioning of the plate thus constitutes a source of considerable expense in the assembly operation. Particularly troublesome is the practical limitation that only the conveyance of thick plates (more than 7 mm) of magnetic material is possible. This disadvantage is all the more serious as the use of aluminum plates, e.g., of a non-magnetic metal in auto body manufacture, is of ever increasing importance.
There remains a need for a new conveyor system for metallic plates, be they magnetic or non-magnetic, which eliminates the above-mentioned disadvantages and assures conveyance of the plates that is mechanically substantially free of possibly harmful contact with the conveyor itself.